Circuit arrangement for producing a vertical frequency deflection current

ABSTRACT

A circuit for generating a vertical frequency deflection current for the electron beams in the picture tube of a television receiver includes a current sensor resistor having one end connected to direct voltage potential by two resistors connected in series and a second end connected to a vertical frequency sawtooth signal by two additional resistors connected in series. An error signal generator has one input terminal connected to the junction the first two resistors and another input terminal connected the junction of the second two resistors. An output stage supplies the deflection current. The output terminal of the error signal generator is connected to the input terminal of the output stage. The error amplifier is a transconductance amplifier having an output terminal connected to reference potential by a series connection of a resistor and a capacitor.

This is a continuation of PCT application PCT/EP 91/00531 filed Mar. 19, 1991 by Rudolf Koblitz and titled "Circuit Arrangement For Producing A Vertical Frequency Deflection Current".

In modern television receivers, the deflection current is generated by means of a class D amplifier. An electronic switch is triggered by pulse width modulated pulses running at line frequency to periodically switch the deflection coils to frame potential using a line transformer. The deflection current is regulated by an error amplifier, the output terminal of which is connected to one of the input terminals of a pulse width modulator. The other input terminal of the pulse width modulator receives a horizontal frequency sawtooth signal. The error amplifier is connected across one diagonal of a resistance bridge, whereby the two input terminals of the error amplifier are connected to a fixed operating voltage by equal size resistors. Also, a direct voltage reference potential and a vertical frequency sawtooth signal, are applied to the input terminals of the error amplifier by two additional resistors which are the same size as the other two resistors. A sensing resistor, having very low resistance, is connected between the two resistors which are connected to the fixed operating voltage. Such an arrangement is disadvantageous in that the bridging resistors, the error amplifier and the DC behavior of the horizontal frequency sawtooth signal are subject to temperature and other environmental changes. Also, the various circuit components have inherent tolerances which frequently negatively impact the stability of the circuit.

It is an object of the invention to eliminate the undesirable effects of such drifting and tolerances so that the stability of the circuit arrangement is reduced to the thermal stability of the resistance bridge and of the input offset behavior of the error amplifier, so that the circuit can be realized by way of integrated circuit technology.

Preferred embodiments are described with reference to the drawings, in which:

FIG. 1 is a first preferred embodiment of the invention.

FIG. 2 is a second preferred embodiment of the invention.

In FIG. 1, a vertical deflection circuit includes vertical deflection coils LV which are connected to an operating direct voltage UB by a current sensor resistor RS which measures the deflection current. The deflection coils LV are switched to reference potential by a controllable electronic switch TH. A winding W of a line transformer ZT and an inductive impedance L connects the switch to the deflection coils LV. The junction of the vertical deflection coils LV and the winding W of the line transformer ZT is connected to frame potential by an integrated capacitor C2. A diode D is connected in parallel to an electronic switch TH to permit a reflux, or free-running operation the circuit. The electronic switch TH is triggered by line frequency pulses which are pulse width modulated so that the intervals during which the vertical deflection coils LV are at frame potential, are adapted to the deflection angle. The line frequency trigger pulses are supplied by a pulse width modulator PBM having two input terminals. The negative input terminal is connected to a horizontal frequency sawtooth signal UH and the positive input terminal is connected to the signal from an error amplifier FV. The error amplifier-FV has two input terminals which are wired in a bridge consisting of two pairs of resistors R1, R1' and R2, R2'. The two resistors R1 and R1' are connected to the operating voltage UB and a capacitor C1. The current sensor resistor RS is located between these resistors. One of the two other branches of the bridge receive a fixed reference potential VDC from resistor R2 and the other branch receives a vertical frequency sawtooth signal UV from resistor R2'. The error amplifier FV regulates the width of the pulses, and thus the deflection current, in such a way that the bridge voltage Ub is zero.

In the FIG. 1 embodiment, a transconductance amplifier, which has the ability to convert an input voltage into an output current, is used as the error amplifier FV. In the example, the transconductance amplifier supplies a current of 1 to 2 mA per 1 V change in input voltage, i.e. it has a g of 1 to 2 mA/V. The output terminal of the amplifier FV is connected to an input stage including an RC network, pulse width generator PBM, and the switching circuit thyristor TH and diode D. The RC circuit is composed of a resistor Ra and a capacitor Ca and is connected to the output terminal of the transconductance amplifier. The RC circuit has a RC time constant in the order of several line times and therefore complete correction is carried out in a few lines. In this embodiment the output stage operates in a D-type operation. In a circuit design tested in practice, a resistance Ra of 33 kOhm and a capacitance Ca of 15 nF were used. A capacitor Cb is parallel to the RC circuit to filter out the remaining line frequency components. In this way, the drift of the horizontal sawtooth signal and the drift of the electronic switch are eliminated. The resistor Ra of the RC circuit supplies the P-portion of the PI controller which also guarantees stability of regulation.

Another preferred embodiment is shown in FIG. 2. In this embodiment the output stage is an amplifier which works in A-B operation. The positive input terminal of the amplifier V is connected to a fixed reference voltage Uref. The signal from the transconductance amplifier FV is connected to the negative, input of terminal of the amplifier V. The same considerations regarding drift and temperature behavior are valid for this arrangement as with the preferred embodiment shown in FIG. 1. 

I claim:
 1. In a circuit for generating a vertical frequency deflection current for the electron beams in the picture tube of a television receiver, said circuit including a current sensor resistor having a first end connected to direct voltage potential by first and second resistors connected in series at a first junction and a second end connected to a vertical frequency sawtooth signal by third and fourth resistors connected in series at a second junction, an error amplifier having a first input terminal connected to said first junction and a second input terminal connected to said second junction, said circuit having an output stage for supplying said deflection current, an output terminal of said error amplifier being connected to an input terminal of said output stage, an improvement wherein:said error amplifier comprises a transconductance amplifier and wherein said output terminal of said error amplifier is coupled via an RC network formed by a series connection of a resistor and a capacitor to a reference potential.
 2. The improvement of claim 1 wherein said output stage operates in a D-operation and further includes a pulse width modulator and an electronic switch means, the output terminal of said transconductance amplifier being connected to said RC network.
 3. The improvement of claim 1 wherein said output stage includes an amplifier working in A-B operation and an electronic switch means, the output terminal of said transconductance amplifier being connected to said RC network.
 4. The improvement of claim 2 wherein the time constant of said RC network is in an order of magnitude of several lines times of said picture tube.
 5. The improvement of claim 3 wherein the time constant of the RC network is in an order of magnitude of several lines times of said picture tube. 